1. Field of the Invention
This invention relates to a two-dimensional suspension for a movable body which translates in a plane.
2. Description of the Prior Art
A two-dimensional suspension (2-D suspension, hereafter) is useful for suspending a movable body which moves under a two-dimensional position control. Especially in an optical information read head, the movable body must be suspended without rotational fluctuation under the tracking and focussing control because the optical performance is reduced by a tilt of the optical axis caused by a rotational fluctuation of the movable body.
Conventionally, a parallel leaf spring is generally employed to suspend a movable body without rotation. The parallel leaf spring usually comprises two leaf springs of the same length and two rigid walls. Each of these rigid walls fixes the opposite ends of the leaf springs at a right angle apart from each other so as not to be on the same plane. In other words, the side view of the conventional parallel leaf spring is rectangular. One of the rigid walls is fixed to a fixing block, and the other is fixed to the movable body. The parallel leaf spring has a high compliance to a translation in a specified direction, and has a low compliance in other directions. Therefore, the parallel leaf spring is useful for suspending a movable body which translates in an arc without rotation. When a movable body translates in a plane, the movable body can be suspended by two conventional parallel leaf springs coupled in series.
The conventional 2-D suspension described above, however, has at least one of the defects as follows:
(i) The connecting member for connecting the parallel leaf springs is so heavy that its resonance interferes with the motion of the movable body;
(ii) The connection of the parallel leaf springs is complicated; and
(iii) The movable body translates in a curved plane because the locus of the translation by the individual parallel leaf spring is an arc.